X-Ray Absorption Spectroscopy on Mixed-Valent Materials

Abstract

X-Ray Absorption Spectroscopy (XAS) has been widely used for the study of mixed-valent (MV) materials particularly near the threshold energy, where direct information on valence admixture may be obtained1,2. However, we must recognize that this technique has not yet proved its ability to test the dynamic properties of the MV ground state. On the contrary, it is commonly accepted that this high energy spectroscopy is unable to give any information on such dynamic properties 3. Moreover the use of the single electron approximation (i. e. the omission of correlation effects between electrons, which may be reflected in multielectron process) to interpret the XAS results is now often criticized 3. It is the aim of our paper to comment on all these points and to consider some further developments of XAS in MV compounds or, more generally, in rare-earth spectroscopy.